A radiant heating system is composed of tubing embedded in flooring, walls, or ceilings of the area to be heated. Heated water is pumped through this tubing to raise the temperature of the surface (thermal mass). Heat energy radiating from the thermal mass heats the objects in the room. As the method of heat transfer in these systems is primarily radiant, lower temperature water is required to heat the thermal mass than is typically needed for convection type systems (e.g., finned tube baseboard heating). In systems where the heat source is not solely dedicated to supplying heated water to the radiant loop, a means of tempering the higher temperature water from a boiler loop, or other type of heating unit loop, is necessary to maintain lower temperature requirements in the radiant loop. An injection loop can perform this tempering by supplying water from the boiler loop to the radiant loop. The amount of heated water injected into the radiant loop can be set using a manually adjusted mixing valve, or using a variable speed injection pump.
In an injection pumping system, the amount of heated water injected into the radiant loop is at the demand of a control system that senses the radiant loop return water temperature and compares it to a specific set point or a difference between the entering water temperature and the returning water temperature. FIG. 1 shows a typical prior art injection system. There are three independent pumps: a boiler pump 10 circulating water in the boiler loop, an injection pump 12 for drawing water out of the boiler loop into the radiant loop, and a radiant loop pump 14 for circulating water through the radiant loop. A manually adjusted balancing valve 16 is typically installed in the injection loop to adjust the percentage of mixing between the injection and radiant loops. An air elimination device (not shown in FIG. 1) can also be installed to avoid entrapped air from affecting the performance of the system. Care must be exercised on installation to make sure that the supply and return junctions 18, 20 in the boiler loop, at which water is drawn into and returned from the injection loop, are not positioned too far apart, as otherwise a “ghost flow” into the radiant loop can occur even when the injection pump is off, as a result of friction-induced differential pressure between the two junctions. A similar ghost flow can occur if the junctions 22, 24 in the radiant loop, at which water is drawn into and returned from the radiant loop, are positioned too far apart. A reference describing such prior art systems is Modern Hydronic Heating for Residential and Light Commercial Buildings, John Siegenthaler, P. E., p. 334 (1995).
The injection and radiant loop pumps, balancing valve, junction fittings, and connecting lengths of pipe can either be assembled in the field, or pre-assembled on a support panel, for example, as disclosed in Lyons U.S. Pat. No. 6,347,748.
The injection pump and radiant loop pump are typically of the wet rotor circulator type. The pump impeller is received in a mating cavity known as a volute. Typically, the volute is surrounded by a flange to which the pump is attached. When the pump is installed, and the impeller thereby positioned within the volute, water enters the pump through an inlet at the center of the volute, and exits through an outlet in the periphery of the volute.
Sometimes multiple radiant loop pumps are used in radiant heating system. In this case, the multiple radiant loop pumps can be installed in volutes formed in a common manifold, as shown in Simensen U.S. Pat. No. 6,345,770. A separate injection pump supplies water from the boiler loop to the manifold.